The invention relates to exhaust fans for exhausting “dirty” or “lab” air (more generically, “inlet” air) and, more particularly, to exhaust fans which mix the inlet air flow with an induced air flow (sometimes otherwise referred to as “dilution” or “rooftop” air).
As a matter of background, exhaust emissions have long been provided with exhaust stacks in order to ensure that the “effective” stack height of the emissions is at least the physical stack height. However, “effective” stack height is more accurately the sum of the physical stack height plus the gains gotten from other effects such as efflux velocity and flowrate, or in other cases buoyancy, and so on. Looked at another way, “effective” stack height is the point where (ignoring buoyancy) the contributions end from such other effects as efflux velocity and flowrate. At that point, the emissions are at the mercy of the dispersions of the localized ambient.
It is an object of the invention to provide exhaust fan systems which minimize physical stack height but through other design factors maximize effective stack height.
It is an alternative object of the invention to achieve the foregoing in combination with mixing an induced or dilution air flow with the given inlet (eg., “dirty” or “lab”) air flow such that the efflux comprises a mixed flow.
It is an additional object of the invention to provide the foregoing with dual driven-impeller packages such that they operate as counterparts to each other. That is, one impeller is optimized for suctioning out the inlet flow from a converging network of ducts having origins in remote diverse intake ports. In contrast, the other impeller is optimized for expelling the mixed exhaust in a tall, columnar plume.
These and other aspects and objects of the invention are provided by an exhaust apparatus for diluting a forced, primary flow of gases with a secondary flow and expelling the consequential diluted flow. One embodiment of such an apparatus comprises the following. That is, it has a passageway for delivering the forced, primary flow. The passageway terminates in an outlet port therefor.
There is also a center body that axially extends from the outlet port to a spaced terminal end. The center body is radially contoured in the axial direction from the outlet port toward the terminal end to include a flaring portion, a convex transition portion, and then a tapering portion. The center body is positioned with respect to the outlet port to accept the delivery of the primary flow to outflow therefrom and be flared out by traversing along the flaring portion.
There is furthermore a windband or, in alternative terminology, a collar. Such a collar axially extends between an input end and a spaced output end. The collar is radially sized to surround the center body and define an annular flow passage therewith. The collar furthermore includes an intermediate hoop section that is sized and disposed to define an annular throat in combination with the center body's convex transition portion.
Given the foregoing, the collar being disposed such that the input end is aimed to channel the outflow of the primary flow from the outlet port toward said throat. Additionally, the collar's input end is spaced away from the passageway's outlet port to allow the introduction of the secondary flow to the primary flow such that the consequential diluted flow flows through said throat and is expelled out the output end.
The invention might more particularly be situated in an environment whereby the passageway comprises an exhaust stack. Such an exhaust stack extends into ambient air and therefore the collar might be reckoned as shaped in a funnel form. That is, from a reference of the hoop section, the funnel form generally flares out toward the input end as well as tapers in toward the output end. In this context, the secondary flow generally comprises drawn in ambient air.
The invention might further be conceived of as including a driven fan downstream from the outlet port for forcing the primary flow. In this context, the primary flow can be reckoned as exhaust gases which are pre-selected to be diluted by ambient air.
In the context of the passageway comprising an exhaust stack, the center body might optionally include a circumferential seam below the convex transition portion for draining adhering rainwater into an interior well. Moreover, the collar might be advantageously shaped to taper toward the output end in spaced correspondence with the center body's tapering portion in order to define an annular nozzle passage sized to forcibly expel the diluted flow.
An alternate embodiment of such an exhaust apparatus operates to combine a forced, first flow of gases with a second flow, thereafter forcibly expel the consequential combined flow. Such an apparatus includes an inventive impeller wheel for forcing the second flow in a direction from a suction side to a pressure side.
Such an impeller wheel includes a hub for rotation about a spin axis, a coaxial rim annularly spaced from the hub and axially extending between a pressure-side edge and a suction-side edge, apertured webbing radially spacing and interconnecting the hub and rim, and angularly spaced blades extending radially out from the rim to tip edges.
A like passageway as described previously is provided for delivering the forced, first flow. Such a passageway terminates in an outlet port, which is disposed to match up closely with the rim's suction-side edge for channeling the forced, first flow to pass through the apertured webbing from the suction side to the pressure side.
Given the foregoing, the blades of the spinning impeller wheel axially force the second flow to annularly wrap around a core of the forced, first flow and thereby afford the flows to combine into the combined flow on the pressure side of the impeller wheel.
This alternate embodiment of an exhaust stack apparatus might optionally include a windband as well, or in alternate terminology, a shroud. Such a shroud would preferably have a circumferential sidewall axially extending between an input end and a spaced output end. It would also preferably have a hoop section that is axially-spaced from the output end. More preferred still is if this particular hoop section is radially-sized and positioned to closely surround a periphery of the tip edges of impeller wheel blades. Overall, the shroud should be positioned such that the input end channels a supply of the second flow toward the impeller blades from the suction side. In consequence, the output end will expel the consequential combined flow.
This alternate embodiment of an exhaust stack apparatus might further be designed as a package including a driven fan downstream from the impeller wheel for forcing the first flow. That way, if the drive for the impeller wheel is adjustable for expelling the diluted flow in substantial flow, the driven fan might be independently adjustable for the loads it is designed to carry in suctioning out exhaust gases from a building or the like.
It is an aspect of the invention that the aforementioned apertured webbing might be realized in any of a variety of designs, including without limitation being designed as angularly-distributed spokes.
A number of additional features and objects will be apparent in connection with the following discussion of preferred embodiments and examples.